Preferential pneumatic grinding and scrubbing of ores and minerals



Oct. 10, 1939. H. E. DUNN 2,175,457

PREEERBETIL PRBUIATIC GRINDING AND SCRUBBING OF 0835 AND MINERALS Filed Nov. 19, 1936 2 Sheets-Sheet "1 .0 Fig.1 7 l INVENTOR f/olber l Ear-l Du I121 .4 4524 6%,flM

' 4.41 JAQQ Oct. 10, 1939.

H. E. DUNN PREFERENTIAL PNEUIATIG GRINDING AND SCRUBBING 0F ORES AND MINERALS Filed 'Nov. 19, 1936 2 Sheets-Sheet 2 INVENTOR PBEFEBEN'I'IAL PNEUMATIC GRINDING AND SCRUBBING F ORES AND LIINEBALS Kolbert Earl 1min, Craiton, Pa., assignor to Vanadium Corporation of America, Bridgeville,

Pa., a corporation of Delaware Application November 19, 1936, Serial No. 111,627

3Clalms.

This invention relates to the preparation oi ores and minerals for subsequent concentration, whereby the usual procedures of fine 'grinc'ing in ball mills, rod mills, pebble mills, disc grinders and the like may be supplemented or entirely eliminated when it is desired to attain the maximum d ee of attrition or wear on the surface of individual grains or groups of grains with a minimum of breaking or rupturing across these 19 grains. The invention is particularly applicable to the removal of adhering coatings of valuable minerals from cores of worthless minerals or of worthless coatings from valuable cores.

Such a procedure becomes particularly desirable ,when the texture of the ore is such that the single grain size to which it is necessary to grind in "order to liberate the locked minerals becomes so small that the usual grinding practices function essentially by breaking across the grains,

resulting in objectionable over-grinding of one or the other constituent or, as is often the case, overgrinding of both constituents, thereby rendering subsequent concentration procedure less effective.

To oil'set these difilculties with existing grind ing methods and equipment, it is customary to make use of screens or classifiers in closed circuit with the grinding equipment in order to remove from the mill the particles that are already sufficiently fine and to return the oversize to the mill to be reground. When screens are used, separation oi the particles depends upon their size, while classifiers separate the particles according to their settling velocity as influenced by their specific gravity and shape. However, the emciency of these devices is not as high as could he wished, and more or less undesirable overgrinct ing results. K

For example, if it is desired to concentrate an ore consisting essentially of a sandstone whose cementing material carries the values 'in the form of soft earthy mineral incrustations on the hard sand grains, and comminution is carried out in the usual manner, it is found that when grinding' has reached the point where, say, 90% of the single grains are liberated, a considerable portion of the sand grain gangue has been reduced by fracturing to such a degree of fineness that its separation from the finely ground values is rendered exceedingly difllcult. On the other hand, ideal comminution, as applied to an ore of this type, would consist in separating the contiguous single grains without rupturing them, then scrubbing, rubbing or abrading away the incrusting mineral values without further fracturing the sand grains, and with little or no wear on the sand grains themselves.

I have found that the objections to prior methods of grinding ores and minerals may be overcome or greatly decreased by introducing the particles of ore to be treated into a compressed air stream and projecting the stream of particles against the walls of an impact chamber made of wear resisting-material in such manner as to cause scrubbing, rubbing, abrading or superficial pulverization of the grains of the particles but not to materially rupture the grains. The stream of particles to be treated is preferably projected against the walls of the impact chamber substantially tangentially of the walls so as to produce a swirling action of the particles which causes them to be rounded and abraded without substantially rupturing them. In this manner, I can scrub the grains of ore free from incrusting mineral values and control to an unusual degree the amount of core fines produced. i

Since air under pressure will discharge from a proper nozzle at a velocity of around 650 feet per second, and the point of contact of the ore parhole with the impact chamber'in the case of angular grains may be initially infinitesimally small, enormous crushing strains may be developed of the order of to times the resisting power of the strongest rock.

Close regulation of the force applied is obtained by controlling the quantity of ore thrown in proportion to the propelling jet; the larger the quantity of ore the more moderate the velocity, at the same time applying no greater initial air pressure than is required to induce rounding of the particles and stripping of the outer layers, unless the particles consist of more than a single grain, when it is desirable, at least during pre liminary passes through the impact chamber to produce breaking through the particles to further free the single grains.

In the accompanying drawings which illustrate a preferred embodiment and modification ofapparatus suitable for carrying out my process;

Figure 1 is a somewhat diagrammatic illustration of the whole apparatus;

Figure 2 is a top plan view of one of the two recessed blocks of wear resisting material which, when assembled together, form the impact chamber;

Figure 3 is a transverse vertical section through the impact chamber taken in a plane corresponding to the line III-III of Figure 2; and

Figure 4 is a viewsimilar to Figure 1, but illustrating a modified form of apparatus in which an air injector is employed for withdrawing the ore particles from the feed chamber and projecting them into the impact chamber.

Referring now more.particularly to the accom panying drawings, and for the present to Figures 1 through 3, the ore to be ground or scrubbed is introduced into a feed chamber 2 through a funnel 3 and conduit 4 provided with a valve 5. Air under pressure is supplied to the top of the feed chamber by means of a conduit 3 connected to a compressedair tank 'I, the flow of air being controlled by valve 8 and the pressure indicated by a gauge 8.

The outlet ID of the feed chamber 2 is con: .trolled by a valve l I and is connected to a flexible conduit I! which may be a rubber hose. The exit end of the conduit I2 is provided with a nozzle l3 which may be of the construction commonly employed in sand blast apparatus. The nozzle projects through the wall of a rubber lined steel housing It inside of which an impact chamber I5 is located. The impact chamber is supported on a grating IS in position to receive the stream of ore and air from the nozzle l3. After the ore particles have been treated in the impact chamber, they are discharged through a cone-shaped passage I! to a receiver It. The receiver l8 and .the impact chamber I! are maintained substantially at atmospheric pressure by connecting a cloth fllterbag 19 to the receiver. The filter .bag releases the incoming air and at the same time prevents the loss of fine particles of ore in suspension. The ore is discharged from the receiver through an outlet 2! controlled by a valve The construction of the impact chamber I5 is illustrated in detail in Figures 2 and 3.- In these figures, the impact chamber is shown in full size. The impact chamber is made of blocks 24 and 25 of hard wear resisting material such as silicon carbide, aluminum oxide. or sintered tungsten carbide or hard metal carbide composition. The blocks are formed with complementary recesses which form an impact chamber 26. The impact chamber has a restricted opening 21 which is located in such position .as to receive the stream of ore and compressed airfrom the nozzle l3, the opening having a diameter of about 2-or 3 times the diameter of the pattern of the projected particles in the plane of the opening. A chamber having an opening 21 of to inch diameter and a bowl 28 oi approximately 1% inch diameter is suiiiciently large to receive a stream of ore particles from a A; to inch nozzle when presented to the stream within a distance of, say, one inch from the face of the nozzle. The stream of ore particles is projected into the chamber 26 substantially tangentially with the wall of the chamber, as indicated by the arrows 29 in Figure 2. The chamber, as will be noted. is. formed-by curved walls forming a chamber which is substantially in the shape of an oblate spheroid. A chamber of the shape or an ovoid or other chamber having rounded walls which cause rotation and swirling of the ore particles may be employed, however.

In carrying out the process with the apparatus shown in Figures .1 through 3, the ore to be treated is charged through the funnel 3 into the receiving chamber 2 while the valve II is closed. when the entire charge has entered the feed chamber, the valve I is closed and compressed air is admitted through the conduit 8. The valve II is then opened and a stream of ore partic s and compressed air is forced through the conduit l2 and nozzle 13 into the impact chamber IS. The treatment in the impact chamber causes abrading or rubbing away of the surfaces of the grains without substantial rupturing of them. The particles of ore striking the walls of the impact chamber lose their velocity almost instantaneously. The particles which have passed through the impact chamber arev discharged through the same opening 21 through which they entered and fall through the grating I6 into the receiver I8.

By applying air pressure to a charge of ore particles in the manner above described, I produce maximum loading of the air blast with ore particles and consequently minimum velocity for the corresponding air pressure used, and consume the minimum quantity of-air. When higher veiocities are necessary and it is found desirable to limit the air pressure, increased velocity may be obtained by the arrangement shown in Figure 4'. In this embodiment, the ore particles are withdrawn from a feed chamber 32 by means of an air inspirator 33. The ore particles are introduced into the feed chamber 32 through a funnel 34 and conduit 35 controlled by a valve 36. A clamp 31 which fits around a piece of rubher tubing 38 connected to the delivery end of the chamber 32 is provided for controlling the flow of ore to the flexible conduit 39, which is provided with a nozzle 40, as in the other embodiment already described. The air injector 33 is connected by an air conduit 4| to a source of compressed air (not shown), and the inspirator is provided with a pressure gauge 42. The remainder of the. apparatus is substantially identical with-that described in connection with the other embodiment. The stream of ore particles is projected into an impact chamber 43 located within a housing 44, and the particles which have been treated in the impact chamber are discharged through a grating 45 into a receiver 43, to which a filter cloth bag 41 is connected.

In either method of feeding the ore, mechanical air locks may be substituted for the manually controlled valves. A multiplicity of impact chambers may be operated from a single feed chamber to provide the necessary capacity, although a single inch noz'zle will treat from 300 to 1800 pounds of ore per hour within its range of velocities for a pressure of 80 pounds per square inch.

As an example of the operation of my process, I may break in crushers and rolls a sandstone having a single grain size between 48 and 100 mesh, to all pass an 8 mesh screen, and charge this material into my preferred apparatus illustrated in Figures 1 through 3, using a inch sand blast nozzle and apply 100 pounds per square inch air pressure. I have found under such conditions, byscreen analysis after a single pass or treatment, that about one-third of all the sizes larger than 48 mesh have been reduced to minus plus 150 mesh grains with only 2% increase in the amount of minus 200 mesh fines present. A second pass results in another one-third reduction of the original content of plus 48 mesh material with a 3% increase in the original minus 200 mesh content, while a third, fourth and fifth Pass produce no sensible further alteration in screen analysis, but have visibly increased the rounding oi. the grains.

By increasing the air pressure to 140 pounds per square inch, the same result is obtained in two passes as required three passes at 100 pounds pressure, but an almost identical screen analysis is maintained even after ilve at 140 pounds pressure as that attained on the second Pass.

The screen analyses in the two' tests just described, were as follows:

ierred i'orm anda modification of apparatus for carrying out my process, it is understood that the invention is not limited to the use of the type of apparatus illustrated or the materials of construction cited, or to the preferred procedure above described, but may be otherwise embodied PNEUMATIC Causnmo Tls'r Fun --8 Mnsn inch diameter nozzle-100 pounds Per square inch air pressure Heads 1st pass 2nd pass 3rd pass 4th pass 5th pass Tyler mesh Weight Cum. Weight Cum. Weight Cum. Weight Cum. Weight Cum. Weight Cum.

Percent Percent Percent Percent Z I Percent Percent Percent Percent Percent 7.34 7.34. 4.11 4.11 1.93 1.98 LU LU 1.12 1.12 1.72 1.72 9. 87 17. 21 5. 39 19. 50 3. 38 5. 81 3. l4 5. 05 -2. 52 3. 74 3. 43 5. 15 5.33 23.54 4. 11 14.51 2.42 7.72 2.52 7.55 1.87 5.61 2. 15 7.30 5. 32 28. 85 3. I) 17.81- 1.98 9.55 1. N 9. 44 1. 50 7. 11 1. 72 9. 02 5. 08 34.94 '4. 11 21. 92 2. 90 :12. 55 2. 52 11. 95 2. 25 9. 36 2. 58 11. 50 7.85 42.79 5.85 28.77 5.8) 18.35 5.55 17.52 5.62 14.98 5.15 15.75 14. 94 57. 73 15. 53 44. so. 15. 94 34. so 15. 35 33. 97 .17. 23 32. 21 15. 88 32. 53 21. 77 79. 50 25; 47 70. 77 31. D 55. so. 18 54. 15 34. 83 57. 04 32. 62 65. 25 9. 87 89. 37 14. 51 85. 38 15. 91' 82. w 18. 86 83.01 15. 35 82. 40 16. 74 81. 99 5.06 94.43 7.31 92.0) 8.70 91.!) 8.81 91.82 9.36 91.76 9. 41 91.43 5. 57 100.00 7.31 100.00 8.70 100.00 8.18 100.00 8.24 100.00 8.57 100.00

inch diameter nozzle 140 pounds per square inch air pressure Heads 1st pass 2nd pass 3rd pass 4th pass th pass Tyler mesh V V Weight Cum. Weight Cum. Weight Cum. Weight Cum. Weight Cum. Weight Cum.

Pe'rceni Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent 7. 34 7.34 2.00 2.00 1.37 1.37 1.18 1.08 1.30 1.30 1.40 1.40 9.87 17.21 v 4.50 6.50 2.74 4.11 2.70 3.78 3.03 4.33 2.34 3.74 6.33 23.54 3.00 9.50 2.28 6.39 2.16 5.94 2.16 6.49 1.87 5.61 5.37 28.86 2.50 12.00 1.83 8.22 1.62 7.56 1.73 8.22 1240 7.01 6.08 34. 94 3.50 15.50 2.74 10.95 2. 70 10.26 2.60 10.82 2.34 9.35 7. 85 42. 79 6. 50 22.00 5. 94 15. 90 5. 95 16. 21 5. 62 16. 44 5. 14 14. 49 14.94 57.73 18.00 40.00 16.44 33.34 15.68 31.89 16.02 32.45 15.89 30.38 21. 77 79. 50 27. 50 67. 50 33. 78 57. 12 32. 43 64. 32 34. 20 66. 66 33. 17 63. 55 9. 87 89. 37 16. 50 84. 00 15. 98 83. 17. 84 82. 16 16. 02 82. 68 17. 29 80. 84 5. 0c 94. 43 8. 00 92. 00 8. 22 91. 32 8.65 90.81 8.66 91. 34 10. 28 91.12 5.57 100.00 8.00 100.00 8.58 100.00 9.19 100.00 8.66 100.00 8.88 100.00

Total 100.00 100.00 100.00 100.00 100.00 100.00

-size has been reduced by six to nine per cent,

practically straight line crushing normally attainable in crushers and rolls only on coarse sizes (plus 8 mesh).

On the other hand, if only scrubbingis desired, I find that at 30 pounds air pressure, no noticeable change in screen analysis is obtained in one pass nor any appreciable rounding of the grains, but at 100 pounds pressure, noticeable rounding is observed on a single pass.

lI'he process may be used to remove surface layers from grains already separated by other means or to separate particles consisting of many grains into those individual grains and then removing the surface layers from each of them. In other words, as previously noted, the process may supplement the comminution processes, or, not only supplement them, but also replace them in part.

Thus, it is apparent that a variety of grinding and scrubbing characteristics may be secured by easily controlled variations in air blast pressure, size of feed and rate of ore feed or loading of the air bast for a given size of nozzle.

While I have specifically described the preand practiced within the scope of the following claims.

I claim:

1. Apparatus for grinding or scrubbing ores and minerals, comprising an impact chamber formed of wear resisting material, a housing for the impact chamber, and means for projecting a stream of compressed air and particles to be treated into the impact chamber, the impact chamber having a constricted opening through which the projected particles enter and exit, the impact chamber having a closed cavern-like bowl -formed substantially in the shape of an oblate spheroid to produce a swirling action and rounding of the particles impacted against it.

2. Apparatus for grinding or scrubbing ores and minerals, comprising an impact chamber formed of wear resisting material, a housing for the impact chamber, means for projecting a stream of compressed air and particles to be treated into the impact chamber, the impact chamber having a constricted opening through which the projected particles both enter and exit, said opening having a. diameter of about two or three times the diameter of the pattern of the projected particles in the plane of the opening, the walls of the impact chamber being curved so as to produce a swirling action of the particles impacted against them, the impact chamber having a bowl of considerably larger diameter than the constricted opening through which the projected particles enter and exit, the bowl being substantlally circular in cross section at its largest diameter.

3. Apparatus for grinding or scrubbing ores and minerals, comprising an impact chamber formed of wear resisting material, a housing for the impact chamber, and means for projecting a stream of compressed air and particles to be treated into the impact chamber, the impact chamber having a constricted opening through which the projected particles both enter and exit, the impact chamber having a bowl in the form of an oblate spheroid and of larger diameter than said constricted opening, said constricted opening having a. diameter appreciably larger than that of the stream of incoming particles.

HOLBERT EARL DUNN. 

